1. Field of the Invention
The present invention relates to a drive circuit for a printing apparatus, a light-emitting element unit, and a printing apparatus.
2. Description of the Related Art
An electrophotographic printing apparatus (laser printer or the like) includes, for example, a photosensitive drum and a light-emitting element for irradiating the photosensitive drum with light. First, the photosensitive drum is charged and irradiated with light by the light-emitting element based on print data. From this operation, the potential of the portion irradiated with light decreases and a potential distribution is formed on the photosensitive drum based on the print data (latent image). Next, toner, which is a colored powder, is adhered to the photosensitive drum. The toner adheres to the photosensitive drum in accordance with the potential distribution on the photosensitive drum (developing). Subsequently, by transferring the toner adhered to the photosensitive drum to a printing medium such as paper or the like, an image according to the print data is formed on the printing medium.
The degradation of the photosensitive drum due to usage of the printing apparatus can change the potential of the photosensitive drum at the time of charging or the potential of a portion on the photosensitive drum which is irradiated with light, and a fog (a phenomenon in which a non-printing region becomes colored) or the like may be generated as a result. This can degrade the image quality. In order to prevent this, Japanese Patent Laid-Open No. 2013-7989 discloses how a light irradiation amount (first amount of light) to a portion on the photosensitive drum to which the toner is to be adhered and a light irradiation amount (second amount of light) to a portion on the photosensitive drum to which the toner is not to be adhered can be adjusted in accordance with the degree of the degradation of the photosensitive drum.
More specifically, according to Japanese Patent Laid-Open No. 2013-7989 (FIG. 5), a printing apparatus includes a light-emitting element 107, a monitor unit (light-receiving element 108) for monitoring the amount of light emitted from the light-emitting element, first current supply units 104 and 105, and second current supply units 114 and 115. For the portion on the photosensitive drum to which the toner is not to be adhered, a current Ib for small light emission is supplied from the second current supply units to the light-emitting element, and light irradiation is performed by using the second amount of light. For the portion on the photosensitive drum to which the toner is to be adhered, currents Idrv+Ib for printing are provided from the first and second current supply units to the light-emitting element, and light irradiation is performed with the first amount of light. The current Idrv of the first current supply units and the current Ib of the second current supply units are controlled based on the monitoring result by the monitor unit and the degree of the degradation of the photosensitive drum. This adjusts the first and second amounts of light. In this manner, according to Japanese Patent Laid-Open No. 2013-7989, the image quality is improved by controlling the respective current values of two kinds of currents, supplying the two kinds of currents to the light-emitting element, and performing printing in accordance with the degradation of the photosensitive drum.
Two current supply units are provided for each light-emitting element in the printing apparatus disclosed in Japanese Patent Laid-Open No. 2013-7989. This arrangement problematically results in a large circuit scale.